The present invention relates generally to fault indicators for alternating current electrical distribution systems, and more particularly to self-resetting fault indicators wherein upon occurrence of a fault the reset circuit of the indicator is actuated before the trip circuit thereof to preclude simultaneous actuation of the two circuits.
Fault indicators of various types have been constructed for detecting faults in electrical power distribution systems. Such indicators include clamp-on type indicators, which clamp directly over cables in the system, and test point-type indicators, which are mounted on test points provided on connectors or components of the system. Fault indicators of both types may be either of the manually reset type, wherein it is necessary that the indicator be physically reset following each fault, or of the automatically reset type, wherein a fault indication is reset upon restoration of line current. Examples of such fault indicators are found in products manufactured by E. O. Schweitzer Manufacturing Company of Mundelein, Ill., and in U.S. Pat. Nos. 4,063,171, 4,234,847, 4,251,770, 4,236,550 4,438,403 and 4,458,198 of the present inventor.
Self-resetting fault indicators typically employ an indicator device, a trip circuit for conditioning the indicator device to indicate a fault upon occurrence of a fault current in a monitored conductor, and a periodically-actuated reset circuit powered by the monitored conductor for conditioning the indicator device to a reset state upon occurrence of normal current in the monitored conductor. Because the reset circuit is actuated at periodic intervals in the presence of current on the monitored conductor, there exists the possibility that the reset circuit will actuate at the same time the trip circuit actuates in response to a fault current, and the indicator will therefore fail to respond to the fault, providing the user with erroneous information that a fault did not occur.